Identifying Regional Viscoelastic Properties of the Superficial Muscular Aponeurotic System

Background: Suspension of the superficial muscular aponeurotic system (SMAS) is generally believed to be necessary in facelift surgery. Although many techniques have been suggested, all rely on the viscoelastic properties of the SMAS Objectives: The aim of this study was to determine the viscoelastic properties of bursting strength, stress relaxation, and creep in the lateral, mid-cheek, and medial regions of the SMAS. Methods: The viscoelastic properties of the SMAS were determined in 12 cadaveric hemifaces. Lateral SMAS was classified as the SMAS overlying the parotid gland; mid-cheek SMAS as anterior to the parotid and overlying the masseter muscle; and medial SMAS as including tissue extending medial from the lateral canthus and ending at the nasolabial fold. Results: The 3 SMAS regions showed significantly different bursting strengths: 38.9 N for the lateral SMAS, 26.7 N for the mid-cheek SMAS, and 11.9 N for the medial SMAS (P <0.0001). Stress relaxation was similar in all vertical regions with measurements of 54% in the lateral, 48% in the mid-cheek, and 59% in the medial SMAS. Creep was found to be similar in the lateral and mid-cheek SMAS with values of 18% and 19%, respectively. The medial SMAS was noted to have a higher creep at 22%. Conclusions: The lateral SMAS has a stronger bursting strength than the mid-cheek and medial SMAS. Creep appears to be lower in the lateral and mid-cheek SMAS. Stress relaxation appears to be similar in all 3 vertical regions.